Long lasting cementless fixation of the femoral component of the hip joint prosthesis remains an unsolved problem. Efforts to do so by surface treatments of the prosthesis stem that would allow bony ingrowth have not resulted in satisfactory clinical results and the cemented femoral component is still considered a better choice for most patients. Current designs of all stemmed hip prosthesis rely on the load transfer by rod-in-tube configuration. The load on the head of the prosthese results in both axial and transverse forces and bending moments (mostly in the frontal plane, but also, and depending on the particular action of the patient, in other planes, generally torsional loads around the long axis of the stem) which must be transferred to bone.
This leads to stem-bone interactions along the stem, which generally compress the medial cortex proximally and the lateral cortex distally. Due to additional muscle loads on predominantly the greater trochanter, bone undergoes significant deformation and it is very difficult if possible at all, to prevent the movements at the prosthesis-bone interface. Bony ingrowth is thus inhibited, and if, and when it occurs, it is limited to only some areas of the interface. At other places motion persists leading to pain, overall instability of the implant and eventual failure. In some cases of porous (bead) coated stems, the bone has been seen to integrate well on the distal parts of the prosthesis, which in turn produced massive bone loss due to stress-shielding.